Recovery of phenol from a constant boiling mixture of phenol and water



Oct. 26, -1937. G. 'l'.I ATKlNs, JR 2,096,871

' RECOVE-RY OF PHENOL FROM A CONSTANT BOILINGrA MIXTURE OF PHENOL yANDWATER f Filed om. 26, 1935 STR 5F52 j v HEA reza Mmm j] y f I2 ToP//ENoL Y Ex TnAcv-o/v wv/r 'Patented oa., ze, 1931 i jUNITED STATES ,I2,096,571 A j nscovsnr or rnENor. 'mou' a consimili` nomme mx'ruan. oram WATER rmmor.

George 'l'. Atkins, Jr., Baytown, Tex., aldtnor'to. Standard OilDevelopment Company. a corporation of Delaware Application mm ze, 1935,lsei-uu No. 6.864

4 Claims.

In recent years the process of refining oils, particularly lubricatingoils, by extracting undesirable constituents with phenol has gained widerecognition as a highly desirable refining step. 5 In general, theprocess consists in treating an oil with phenol at a temperature atwhich phenol is liquid, whereby two layers of liquid are formed, the onelayer, known as the extract, containing most of the phenol and theundesirable constituents extracted from the oil, and the other layer,known as the raffinate, consisting of the refined oil and up to about20% phenol. The phenol is then recovered from both the extract and the.

' raffinate by distillation. Afterdistillation the rafnate is usuallysteam-stripped to remove the last traces of phenol. l

During the extraction with phenol any water in the oil associates itselfwith the phenol both in the extract and in the railinate. In therecovery ofV phenol from the raflinate and extract i vby distillation,any water in either portion of the oil forms with the phenol a lowerboiling mixture than the phenol itself. Consequently, a water phenolmixture is taken oiI. as an overhead in these. distillations and purephenol is taken oil! y preferably las a side stream. In addition. a fur--ther amount of phenol water mixture is obtained by the steam-strippingof the raffinate, As a result the process is accompanied by theaccumulation of large quantities of phenolic water containingsubstantial amounts ofphenol. In order to realize the full benefit ofthe process as a whole and to put it on a practical, basis, it isnecessary to revover the phenol from the phenolic water. It is to such arecovery process that this. invention is directed.

The separation of phenol from phenolic water presents a diilleultproblem.l The volatility of phenol, when dissolved in water, isabnormally high, so that the separation of these two substances bydirect distillation cannot be completely effected even whenextraordinary care is exercised.A .0n the other hand, the afiinity ofphenol lfor water is suiiiciently 'strong that the treatment of anaqueous solution of phenol with any of those solvents which, up to thepresent, have been found to be selective for phenol, will not eiectasatisfactory separation of the phenol from the water.

Prior to the present invention the methods of recovery had been reducedto two which were selected, not because they were eminentlysatisfactory, but because, although each one was at- Y tended by manyobjectionable features they were 55 the most satisfactory thathad beenevolved. Of

(Cl. 26o-154) v these methods, the most commonly employed labor chargeto the' phenol extraction process as a whole, it introduces into theprocess an additional ingredient which is lost in the performance Y, ofits function, and it results in .a satisfactory recovery of phenol onlyat the expense of purity. 10

The above enumerated and other objectionable features of the salting outprocess led to an investigation of the possibility4 of recovering phenolfrom phenolic water by distillation under vacuum. After considerableexperimental work it was found possible by this method to reduce theamount of phenol in phenolic water from about 10% to between 2.9 and3.5% by the employment of a vacuum of from l0 to 20 mms. This recoverywas not quite as good as could be obtained bythe salting out process.This decreased recovery was compensated, however, by the fact that the,vaccum distillation is a continuous process and does not require theintroduction into the process of extraneous materials. On the other handthe best recovery could be obtained only in a distillation tower of lowcapacity and with an extrmnely careful regulation of operatingconditions. A fair conception .of -the diiiiculty of control attendingrecovery by vacuum distillation can be obtained by consideration of thefacts that under an absolute pressure of 10 mms. of mercury the dierencebetween the boiling point of water and that of a 70% aqueous solution ofphenol is only y 2 F., and the difference between the boiling points ofthe same liquids 'under 20 mins. of

- mercury and under 50 mms. of mercury is only The present invention, inlits mostspecific aspect, is based yon a reaiization'of the fact that,when phenolic water is vaporized, the special amnity of the twocomponents for each other disappears, whereby, by the choice of asuitable solvent, the phenoLvapor can be readily separated from'theVwater vapor. Practical considerations instantly point to the use, as asolvent for this purpose, of the oil which is to be phenol extracted.This expedient simpliiies the phenolic extraction process as a whole,makes possible a `more complete recovery of phenol from phenolic waterthan was hitherto attainable, and, in effect-A ing the recovery ofphenol, places it directly in its proper functional relationshipwith theoil for the phenol extraction process. However, in some cases it mightbe desirable to use the phenol-free 2 t l Y 0,000,871

extract as the solvent, returning this solvent, together with dissolvedphenol, to the distillation process' for separating extract and phenol.VThe merits of this procedure would be that-the ratio oi.' solventto-phenolic water in the absorbing tower could be varied independentlyof other operating conditions and could be as high as desirable (withinthe capacity limits of the equipment used), vand that the extractpossesses a greater ailinity for phenol than does the untreated oil. Amore complete recovery of phenol would result from the increased ratioof solvent to phenolic water, and from the greater solvent power of theextract.

If it be desired to recover phenol as a solid in its pure state, it ispreferable to employ, as the scrubbing agent for the phenolic ,watervapors, a pure chemical compound having a single fixed boiling pointwidely removed from that of phenol, or having a tlxed melting pointsubstantially diil'erent from that of phenol whereby the phenol can berecovered from the scrubbing agent by distillation or crystallization.Examples` of such pure compounds as may be employed are naphthalene,ortho-toluidine and alkyl derivatives of aniline. Generally, however,there is a suillcient difference between physical properties of phenol Yand lubricating oil itself to render the use of lubricating oil entirelyfeasible when it is desired to recover phenol as a solid in its purestate.

The principle involved is the separation of a constant boiling mixture(in which the partial pressures `of both components are abnormally highas judged by Raoults law) by the production of a liquid phase in whichone of the components, A, (such as phenol) will have a partial pressureapproaching as a minimum the partial pressure predicted tby Raoults law;and in which the other component, B, (such as water) will have a.partial pressure greater than that predicted by Raoults law and agreater positive deviation from Raoults law than it had in the cmstantboiling Under Y these conditions the vapor evolved is richer incomponent B than was the original mixture The absorbent, C, (such as ahigh-boiling mixture of hydrocarbons) need not possess chemical ailinityfor either component, but will exert its solvent power for-component Asolely by virtue of establishing a liquid phase in which component Amore nearly obeys Raoult's law. In selecting an absorbentwhich will havethis property, it is convenient to consider the internal pressures, orthe dielectric constants, or thesolubillties in some referencesubstance, of the two components and of the absorbent; or to considerpublished lists (Hildebrand. Chemical Catalogue Co., 1924) of sulntancesbased on the above properties suclrthatsubstanceshavingsimilarvaluesoftheseproperties and standing adjacent inthese lists form solutions showing onb small departures fran Raoultslaw, whereas substances having dinerent valuotthesepropertiesand'standingfarapartin these lists show largedepartures from Raoults law. These properties and lists are mentioned,since those absorbents are usually-particularly eil'ective which standin such lists in'theorder BAC; especiallywhere thepropertyconsideredisinternalpresaure at the distillationtemperature(orlatentheatofvaporixationperunitvolmneof liquid)andwheretheinternalprmeotBis greaterthanthatotmandtheinternalpressureofAisgreaterthanthatofCbutnearlyellualto thatofone liquidphasepresent.Theremaybe one,two,orthreeliquidphaseainccntact,butit is necessary andsufcient that one liquid phase be produced in which component A shallhave a smaller positive deviation from Raoults law then it (component A)has in the mixture of A and B to be separated. l

In general, the solvent selected in any given instance, for theseparation of one component from a mixture thereof with one or moreother components, should have the following properties:

1. It should be a liquid at the temperature oi' operation,

2. It should be substantially non-volatile at these temperatures, or atleast have a low volality. Y.

3. It must be a good solvent for one of the components,

which is sought to be extracted from the mixture can be employed.- Itssolvent action for the other components of the mixture shouldnotincrease unduly as the selected component dissolves in it,

6. It must be possible to recover the dissolved componentv from thesolvent without undue ditlicult?.

7. It must be stable.

In its preferred form the process, according to the present invention,is carried out by introducing a vapor mixture of phenol and water to thebottom of a scrubbing tower into the top of which a scrubbing agent isintroduced. 'I'he scrubbing agent is usually introduced at a temperatureabove the vaporization point of water. The temperature in the towershould not be allowed to exceed that at which the phenol will dissolvein it. In general, when the process is-conducted under atmosphericpressure the phenolic water vapor enters the tower at a temperature upto about 270 F., preferably between 230 and 250 F., and the scrubbing`agent enters vthe tower at a temperature up to 230 F., preferablybetween 213 and 225 F., although it may be introduced at atemperaturebelowtheboilingpointofwatersolons as it is not introduced atsuch temperatures in sumcient quantities to reduce the temperature ofthe vapors in the tower below the condensing point of water.

Iftheoriainal vaporisveryrich inphenol itis preferable tn partially coolthe vapor so as to deposit liquid phenol containing only a small amountof water. This condensate is easily dehydrated by boiling. The leanvapor can then be subjected to scrubbing. This initial condensation hasthe advantage that it will leave a vapor which has a condensationtemperature about that of water. Thisvvapor should then be scrubbed at atemperature as little as possible above 212' 1"., as a low scrubbingtemperature always increases the solubility of the phenol in the oil. Y

-Theprocessmaybeconductedunderany desired pressure. The chief advantageof employing rey 2,096,871 water, the greater will be the percentagerecoveryl oi' phenol. The only upper limit on the quantity of scrubbingagent employed is a practical limit determined by balancing Aphenol`losses against cost of equipment, plant capacity, and operating In theaccompanying drawing in which a plant, suitable for the carrying out ofthe process according to the present invention, is illustrateddiagrammatically, a steam phenol vapor mixture is introduced throughline I into a scrubbing tower' 2 which may be packed with a suitablefilling material, such as Raschig rings, or provided with interiorconstruction, such as baille plates or discand-doughnut plates.scrubbing oil is fed to the top of tower 2 through line 3. Steam isdischarged from tower 2 through line l, and may be sent in aconventional manner through preheaters for the recovery of its heat.

The phenol dissolved in the scrubbing medium v vdifferent pressures withintermediate separation leaves tower 2 through line 5, and is dischargedinto a stripping tower 6 in which it ilows` downwardly incounter-current to a hot inert gas introduced through line 1 whereby itis stripped of any absorbed water. The inert gas leaves stripeping tower5 through line' 8, passes through a condenser 9 in which it is separatedfrom any steam and phenol which it carries over, and then passes throughline I0 back to line 1 for recycling. The water. containing some phenolrecovered in condenser 9, is passed through preheater I0 where it isvaporized and then passed into line I with the fresh phenolic watervapors.

'Ihe dry solution of phenol in oil leaves tower 6 through line II inwhich it may be conducted directly to a phenol extraction unit. In theevent that it is desired to recover pure phenol, the oil solution ofphenol is conducted through line I2 to a preheater I3 in which it isheated to a temperature above the vaporizing temperature of phenol, andis then ilashed into a rectifying tower Il.' To facilitate therectification, inert gas from supply line 'I is introduced into thebottom of tower I4 through lixie i5. The inert gas, carrying vapors ofphenol, leaves tower I4 through line I6, passes through condenser I'Iinto a separator I8 from the bottom of which phenol is drawn off throughline I9 and from the top of which inert gas is recycled through line-20baci; to supply line-1. Scrubbing oil, or other medium, leaves tower Ilthrough line 2| in which itis conf ducted back to feed line 3.

The process, according to the present invention, may be furtherillustrated by the following data obtained from a series of runs inwhich phenolic water, containing approximately 9.6% or phenol by weight,was fed tothe scrubbing tlower at a rate of approximately '100 ccs. per

our.

brieaung stock having a. gravity f23.5 A. P. I."

and a ash oi: 520 F. In Runs 6, 7, 8 and 9 the oil containing theabsorbed phenol leaving tower 2 was substantially dry and was suitablefor direct addition to the phenol extraction unit without being strippedby inert gas. Y Run 2 illustrates the effect of maintaining the bottomof the scrubbing tower at too high a temperature. Run 4 is included todemonstrate the eiect of the ratio of oil to phenolic water on thepercent of phenol recovered. Run 8 demonstrates the importance ofemploying, as a scrubbing medium, a substance oi' high mobility, the oilused in Run 8 having been more viscous than the oil employed in theother runs. The effect of this higher viscosity was particularlynoticeable because .the run was conducted under a partial vacuum andcorresponding low temperatures.

' The advantages of this method of separation, as compared to separationby distillation under of liquid phases, are:

(l) Lower reflux ratios can be used resulting in smaller tower diametersand lower heat inputs,

(2) Fewer trays of bell-caps need be installed because of sharperseparation,

(3) The entire process can be performed at atmospheric pressure,

(4) No separation of liquid phases with'intermediate cooling isrequired,

(5) Only one tower is required for the removal of water, so that in thephenol treating ofy lube oils, the oil-phenol mixture can be separatedin the main equipment, v

(6) No chemicals for salting out" are required.

While the present invention has been described with particular referenceto phenolic water obtained from a phenol extraction process, it isobvious that the particular source of the phenolic water is of nospecial significance in the measurement of the scope oi the process. Itis to be understood also, that, while the specific method of recoverydescribed above is possessed of unusual merit when employed inconjunction with a phenol extraction plant and in such a combinationconstitutes the preferred form of the present invention, the applicationof the present invention is in no way limited to a phenol extractionplant, or to the 'recovery of phenol vfrom phenolic water by an oilwhich is subsequently to be extractedfwith phenol,- but is general innature and embraces the recovery of phenol from phenolic water from anysource by .extracting the phenol from a vapor mixture thereof with waterby scrubbing with any solvent for phenol which is immiscible with waterand which is liquid at the temperature oi' the phenol-water vapormixture.

Applicant contemplates within the scope of his Bun N0 1 2 3 4 5 6 7 8 9l0 Oil/phenolic water ratio by voi. 3. 9 4. 2 5. 2V l. 8 5. 0 7. 8 6. 77. 0 7. 3 7 Percent phenol in overhand 1. 55 2. 7 0. 81 3. 95 l. 48 0.82 l. l l. 8 l. 0 0. 6 Percent phenol recovery 88.3 74.0 94.0 61.0 8 7`93.9 89.0 81.5 90.0 94.0 Flash temp v F-. 254 246 225 235 230 232 145220 145 140 Bottom temp F-- 224 273 225 237 257 250 lill 170 145 143 Oilfeed imm F 197 223 225 226 218 213 110 180 125 119 Vapor temp F-- 216216 215 215 215 215 im 1w 135- 140 Pressure-mm. nbs Atmospheric 88 367136 143 The oil employed as a scrubbing medium in -invention not onlythe separation oi' phenol from each run, except Run 8, was an untreatedlubrieating stock suitable for phenol extraction having'a gravity o!24.5 A. P. I. and a iiash of 440 F. In Run 8 the scrubbing medium was aluwater,- b ut the'separation from aqueous solution of substances, suchas the cresois which, while they have a considerably higherboiling'point than that of water, are readily volatile in steam watermay be mentioned. The separation o! non-aqueous mixtures is alsocontemplated.

"Rie nature and objects oi the present invention havingbeen thusdescribed and practical embodiments o1 the samehlving'been given withoutany intention of thereby deiining the scope oi said invention, what isclaimed as new and useful and desired to be secured by Letters Patentis: l

1. In the extraction ot an oil with phenol in which an extract and arailinate are formed and phenol is recovered therefrom with theformation of a constant boiling mixture of phenol and water, the stepswhich comprise vaporizing the mixture of phenol and water and contactingsaid vapors at a temperature sumcient to maintain them in the vaporstate with oil whichvis to be extracted with the phenol, and separatingsaid the oil is conducted under sub-atmospheric' 4. In the extractionoan-oil with phenol in which isn-extract and a railinate are formed andphenol is recovered therefrom? with` the formation .of a constantboiling mixture oi' phenol and water, the steps which comprisevaporizing the mixture oi phenol and wate contacting said vapors at atemperature suilicient to maintain them in a vapor state with amenstruum selected from the group consisting oi' the oil which is to beextracted with the phenol and the extract obtained after removaltherefrom of the phenol and separating the mens'tmum with its dissolvedphenol from the treated vapors.

GEORBB T. ATKINS, JR.

